1. Field of the Invention
The present invention relates to a novel method for fabrication of homogeneous sol gel-derived multi phase materials, especially ceramics, and gelling control agents therefor, and more particularly relates to a novel method for fabrication of homogeneous sol gel derived SiC/Al.sub.2 O.sub.3 composites and the particular gelling control agents therefor.
2. Description of the Prior Art
This invention provides a unique way to fabricate a variety of sol gel derived materials that require homogeneous mixing of two or more constituents. These are referred to as multi-phase or composite materials where the gel provides a matrix in which the reinforcement materials are distributed and held. Sol gel processing is known as a potentially good method for preparing such multi-phase materials, see copending applications Ser. Nos. 583,737; 583,738; 583,743; and 583,745 filed Feb. 27, 1983, all of the stated applications being now abandoned. Fabrication of the composite is accomplished by mixing fibers, whiskers or particulates into a low viscosity sol just prior to gelation. Upon gelation, these reinforcement materials ar "frozen" into the structure. Subsequent drying and firing will result in a strong and tough ceramic composite. A significant problem with this method of fabrication is that the settling of the dense reinforcement materials due to gravity can lead to their segregation prior to gelation. If this occurs, the resulting dried and fired ceramic composites will not be homogeneous. That is, the reinforcement materials will not be distributed uniformly throughout the matrix. In order to prevent segregation, the reinforcement materials must be mixed with the sol just prior to elation. This degree of control is not easy to maintain, even on a laboratory scale.